[R] How to....

[Jia Ying Mei]

Thank you very much. As for the second part, for every price change, the 
percentage of every price change can be calculated (i.e. amount of 
change divided by previous price). I was looking for a way to merely 
find the mean and median of all price change percentages for each 
country. I don't know if that's helpful or not. But thats very much for 
the first part, thats the harder part for me I think.

Jia Ying Mei

Jim Lemon wrote:
> On Tue, 2008-07-22 at 16:31 -0400, Jia Ying Mei wrote:
>   
>> Hi everyone,
>>
>> I am not new to R, but its been over a year since I've used it, so I 
>> don't remember how to do some things.
>>
>> I have a data set (in excel currently, but will be converted to text), 
>> that has date, country and price, with a price for every country for 
>> every date. I need to find the mean and median of the interval between 
>> price changes for each country and the mean and median percentage change 
>> for each price change within the data for a single country.
>>
>> How should I go about doing this? I'd appreciate any help.
>>     
>
> Hi Jia,
> I'm not too sure what you mean by the second set of means and medians,
> but this should get you started:
>
> # first make up some data
> jym.df<-data.frame(country=rep(c("au","br""cn","in","us"),each=100),
>  date=rep(as.Date("02/02/2008",
>   format="%d/%m/%Y"),500)+sample(-40:40,500,TRUE),
>  price=rnorm(500,100,20))
> # get the intervals by country - have to create a new data frame
> jymint.df<-data.frame(country=rep(levels(jym.df$country),each=99),
>  intervals=unlist(tapply(jym.df$date,jym.df$country,diff)))
> library(prettyR)
> # break down the intervals by country
> brkdn(intervals~country,jymint.df,num.desc=c("mean","median"))
>
> Jim
>
>
>